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Temperature Depdendent Electrical Conductivity acting weird.
Posted 16 ott 2012, 18:10 GMT-4 2 Replies
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Hi Everyone,
I have two simple questions that I have been unable to answer after trying to work on them for a week. Please help me:
1) I have a very simple model (which I have attached), I am passing a few Milli-amps through my geometry and observing how the material is heating up and seeing how two things in particular are affected: The thermal conductivity k and the electrical conductivity sigma. The material I am using is polysilicion from the model library in Comsol. Both sigma and K are temperature dependent; the thermal conductivity is producing a reasonable result. However, electrical conductivity is a constant through out the domain, even though the equation for sigma is temperature dependent. The changes in temperature are big enough that I should see a complicated profile of electrical conductivity rather than just a constant. As a a result, the resistance of a material is a constant throughout which I know from experiment is not true.
I have tried using my own equations for electrical conductivity but with no success. Can anyone please advise as to what could be going wrong? The attached model is simple enough that anybody should be able to look at it in a few minutes and tell me what I could be doing incorrectly.
2) I have heat transfer as one of my physics models and under heat source in that model, I have the option to use "electromagnetic power loss density (ec/cucn1)" (which I heard is similar to joule heating). Can any please tell me what cucn1 means or where I can find its definition?
Any, I repeat, any help would be tremendously appreciated.
-Ammar.
I have two simple questions that I have been unable to answer after trying to work on them for a week. Please help me:
1) I have a very simple model (which I have attached), I am passing a few Milli-amps through my geometry and observing how the material is heating up and seeing how two things in particular are affected: The thermal conductivity k and the electrical conductivity sigma. The material I am using is polysilicion from the model library in Comsol. Both sigma and K are temperature dependent; the thermal conductivity is producing a reasonable result. However, electrical conductivity is a constant through out the domain, even though the equation for sigma is temperature dependent. The changes in temperature are big enough that I should see a complicated profile of electrical conductivity rather than just a constant. As a a result, the resistance of a material is a constant throughout which I know from experiment is not true.
I have tried using my own equations for electrical conductivity but with no success. Can anyone please advise as to what could be going wrong? The attached model is simple enough that anybody should be able to look at it in a few minutes and tell me what I could be doing incorrectly.
2) I have heat transfer as one of my physics models and under heat source in that model, I have the option to use "electromagnetic power loss density (ec/cucn1)" (which I heard is similar to joule heating). Can any please tell me what cucn1 means or where I can find its definition?
Any, I repeat, any help would be tremendously appreciated.
-Ammar.
Attachments:
2 Replies Last Post 19 ott 2012, 15:24 GMT-4
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Posted:
1 decade ago
Hi,
The reason that you do not see any variation in the electrical conductivity, even though it depends on the temperature, is that the Electric Currents part of the model does not use the temperature field that the Heat Transfer in Solids part computes. To couple the two together to simulate the ohmic heating (Joule heating), go to the settings window for Electric Currents > Current Conservation and, under Model Inputs, change the Temperature from "User defined" (using a constant temperature of 293.15 K) to Temperature (ht/ht) to use the temperature field from the Heat Transfer in Solids (ht) physics. You should also use a heat source Q that is the "Total power dissipation density (ec/cucn1)" to get the heating effect from the electric current.
Regarding the "(ec/cucn1)" suffix, it indicates that this heat source comes from the Electric Currents (ec) physics' Current Conservation 1 (cucn1) node. To see the tags ("ec" and "cucn1") in the Model Builder, choose, for example,
View>Model Builder Node Label>Show Name and Tag
You can see the definition of the total power dissipation density in the settings window for the Equation View subnode to the Current Conservation 1 node (to activate Equation View, select it from the "Show" menu in the Model Builder window's toolbar). It is defined as the resistive losses ec.Qrh, which in turn is defined as
ec.Jx*ec.Ex+ec.Jy*ec.Ey+ec.Jz*ec.Ez (that is, "J dot E")
Best regards,
Magnus Ringh, COMSOL
The reason that you do not see any variation in the electrical conductivity, even though it depends on the temperature, is that the Electric Currents part of the model does not use the temperature field that the Heat Transfer in Solids part computes. To couple the two together to simulate the ohmic heating (Joule heating), go to the settings window for Electric Currents > Current Conservation and, under Model Inputs, change the Temperature from "User defined" (using a constant temperature of 293.15 K) to Temperature (ht/ht) to use the temperature field from the Heat Transfer in Solids (ht) physics. You should also use a heat source Q that is the "Total power dissipation density (ec/cucn1)" to get the heating effect from the electric current.
Regarding the "(ec/cucn1)" suffix, it indicates that this heat source comes from the Electric Currents (ec) physics' Current Conservation 1 (cucn1) node. To see the tags ("ec" and "cucn1") in the Model Builder, choose, for example,
View>Model Builder Node Label>Show Name and Tag
You can see the definition of the total power dissipation density in the settings window for the Equation View subnode to the Current Conservation 1 node (to activate Equation View, select it from the "Show" menu in the Model Builder window's toolbar). It is defined as the resistive losses ec.Qrh, which in turn is defined as
ec.Jx*ec.Ex+ec.Jy*ec.Ey+ec.Jz*ec.Ez (that is, "J dot E")
Best regards,
Magnus Ringh, COMSOL
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Posted:
1 decade ago
Hey,
wow Thank you, perfect answer. I now have a solid grasp over what I am doing.
Thank you very much!
-Ammar.
wow Thank you, perfect answer. I now have a solid grasp over what I am doing.
Thank you very much!
-Ammar.